* Add squashfs with LZ4 and LZO compression to Barebox
* Add squashfs with LZO compression to U-Boot
* Use "raw" as type for kernel partition which is compatible with ext4
image as well as squashfs.
Note: This does not use squashfs for the kernel but merly adds support
for it. This will allow to downgrade/fallback to the non-squashfs
version. Using squashfs for the kernel partition is implemented in dev
(for release 7).
The change "Avoid trying to boot non-existing kernel image in failover
case" introduced a broken boot script on Raspberry Pi (when booting from
partition B) and ODROID-XU4.
* Avoid trying to boot non-existing kernel image in fail-over case
The A/B update system automatically switches to the other boot slot when
booting fails. However, in a fresh installation, only boot slot A
exists. If booting fails three times (e.g. if somebody plugs out power
before the slot can be marked as good), then the system switches to boot
slot B which does not contain a kernel image yet. Avoid trying to boot
the non-existing kernel image.
With this change, if slot B is empty U-Boot will restore both slots to 3
attempts and retry booting from slot A on next reboot:
```
Trying to boot slot B, 2 attempts remaining. Loading kernel ...
** Unrecognized filesystem type **
No valid slot found, resetting tries to 3
storing env...
```
Co-authored-by: Pascal Vizeli <pascal.vizeli@syshack.ch>
